Battery case for secondary battery

ABSTRACT

Disclosed herein is a battery case including a receiving part having an electrode assembly mounted therein, wherein the receiving part, which is formed by deforming a sheet type base material, is configured to have a stair-like structure in which at least one corner and/or surface forming a shape of the receiving part is deformed.

TECHNICAL FIELD

The present invention relates to a battery case for secondary batteriesof a novel structure and, more particularly, to a battery case includinga receiving part having an electrode assembly mounted therein, whereinthe receiving part, which is formed by deforming a sheet type basematerial, is configured to have a stair-like structure in which at leastone corner and/or surface forming a shape of the receiving part isdeformed.

BACKGROUND ART

A secondary battery has been widely used as a power source for mobiledevices, such as a mobile phone, a laptop computer, and a camcorder. Inparticular, the use of a lithium secondary battery has been rapidlyincreased because the lithium secondary battery has high operatingvoltage and high energy density per unit weight.

Based on the construction of electrodes and an electrolyte, the lithiumsecondary battery may be classified as a lithium ion battery, a lithiumion polymer battery or a lithium polymer battery. In particular, thelithium ion polymer battery has been increasingly used because thelithium ion polymer battery has a low possibility of electrolyte leakageand can be easily manufactured.

The lithium ion polymer battery (LiPB) is configured to have a structurein which an electrode assembly manufactured by thermally weldingelectrodes (cathodes and anodes) and separators is impregnated with anelectrolyte. Generally, the lithium ion polymer battery is configured tohave a structure in which the electrode assembly is mounted in apouch-shaped battery case formed of an aluminum laminate sheet in asealed state. For this reason, the lithium ion polymer battery is oftenreferred to as a pouch-shaped battery.

FIG. 1 is a view typically showing a general structure of arepresentative secondary battery including a stacked type electrodeassembly.

Referring to FIG. 1, a secondary battery 10 is configured to have astructure in which an electrode assembly 30, including cathodes, anodesand separators disposed respectively between the cathodes and theanodes, is mounted in a pouch-shaped battery case 20, cathode and anodetabs 31 and 32 of the electrode assembly 30 are welded to two electrodeleads 40 and 41, respectively, and the electrode assembly 30 is sealedin the battery case 20 in a state in which the electrode leads 40 and 41are exposed to the outside of the battery case 20.

The battery case 20 is formed of a soft wrapping material, such as analuminum laminate sheet. The battery case 20 includes a case body 21having a hollow receiving part 23, in which the electrode assembly 30 islocated, and a cover 22 connected to the case body 21 at one sidethereof.

The electrode assembly 30 of the secondary battery 10 may be configuredto have a jelly roll type structure or a stacked/folded type structurein addition to the stacked type structure shown in FIG. 1. The stackedtype electrode assembly 30 is configured to have a structure in whichthe cathode tabs 31 and the anode tabs 32 are welded to the electrodeleads 400 and 410, respectively.

The battery case 20 of the secondary battery is manufactured by pressinga sheet type base material, e.g. a base material of an aluminum laminatesheet, using a punch formed in the shape of a rectangular parallelepipedcorresponding to the receiving part 23 and cutting the deformed sheettype base material so as to have a size corresponding to a cover in thelongitudinal direction of the receiving part 23 and to a gas pocket inthe lateral direction of the receiving part 23.

In recent years, however, a new type of battery cell is required inaccordance with a slim type design trend or various other design trends.On the other hand, conventional battery cells are configured to includeelectrode assemblies having the same size or capacity and battery casescorresponding to the electrode assemblies. For this reason, in order tomanufacture a battery cell of a novel structure in consideration of thedesign of a device, to which the battery cell is applied, it isnecessary to reduce the capacity of the battery cell or change thedesign of the device so that the size of the device is increased.

In addition, electrical connection is complicated during change indesign of the device, and therefore, it is difficult to manufacture abattery cell satisfying desired conditions.

Meanwhile, for a secondary battery, an electrode assembly is mounted ina receiving part, the receiving part is covered by a cover such that thereceiving part is sealed, a contact portion between the cover and a mainbody is thermally welded, and an activation and aging step is performed.In order to remove gas generated at this time, the activation step isperformed in a state in which a battery case having a gas pocket isprimarily sealed. The gas is removed through the gas pocket, sealing isperformed again according to the size corresponding to the receivingpart, and the gas pocket is cut off. In this way, the secondary batteryis manufactured.

In the pouch-shaped battery, however, a base material extends in athickness direction of the receiving part in a state in which stress isinherent during pressing of the base material using a punch to form thereceiving part with the result that it is difficult to accurately form aforming width of the receiving part. The thickness direction of thereceiving part means the vertical direction or the direction in whichthe electrodes of the electrode assembly are stacked in the receivingpart and the forming width of the receiving part means the width of thereceiving part formed in the direction perpendicular to the thicknessdirection of the receiving part.

That is, when the base material is pressed to have the shape of arectangular parallelepiped, wrinkles A or chlorosis B occurs at thecorners of the receiving part as shown in FIGS. 2 and 3 with the resultthat moisture may penetrate into the battery.

Therefore, there is a high necessity for a technology that is capable ofsecuring the space of a receiving part, in which electrode assembliesformed in various shapes are mounted, while fundamentally solving theabove problems.

DISCLOSURE Technical Problem

Therefore, the present invention has been made to solve the aboveproblems, and other technical problems that have yet to be resolved.

Specifically, it is an object of the present invention to provide abattery case including a receiving part corresponding to electrodeassemblies formed in various shapes to exhibit high power and largecapacity.

It is another object of the present invention to provide a battery casein which a portion of a sheet type base material at which a receivingpart is to be formed is pressed by a punch formed in a novel shape toform the receiving part, thereby improving accuracy of the receivingpart and securing safety.

Technical Solution

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a battery caseincluding a receiving part having an electrode assembly mounted therein,wherein the receiving part, which is formed by deforming a sheet typebase material, is configured to have a stair-like structure in which atleast one corner and/or surface forming a shape of the receiving part isdeformed.

In a conventional battery case, a receiving part, in which an electrodeassembly is mounted, is configured to have a structure in which theplanar shape of the inner circumference of the receiving part issymmetric with respect to a central axis of the receiving part or tohave a structure in which the vertical sectional shape of the receivingpart is straight at flat side surfaces and a lower end of the receivingpart. For example, the planar shape of a cylindrical type or coin typebattery case is symmetrically circular, and the vertical sectional shapeof the cylindrical type or coin type battery case is straight at theside surfaces and the lower end of the battery case. Also, the planarshape of a prismatic or pouch-shaped battery case having a thinhexahedral structure is symmetrically square or rectangular, and thevertical sectional shape of the prismatic or pouch-shaped battery caseis straight at the side surfaces and the lower end of the battery case.

On the other hand, the battery case according to the present inventionis configured to have a stair-like structure in which at least onecorner and/or surface forming the shape of the receiving part isdeformed unlike the conventional battery case.

In the present invention, therefore, the “corner and/or surface isdeformed” means that the planar shape of the inner circumference of thereceiving part is not symmetric with respect to a central axis of thereceiving part and/or the vertical sectional shape of the receiving partis not straight at at least one selected from among the side surfacesand the lower end surface of the receiving part.

Such deformation may take various forms as will be described below.Deformation satisfying the above conditions must be interpreted to fallwithin the scope of the present invention.

The base material may be formed of a laminate sheet including a metallayer and a resin layer suitable for, for example, a pouch-shapedbattery. Specifically, the base material may include an upper layer of afirst polymer resin, an intermediate layer of a blocking metal and alower layer of a second polymer resin. Specifically, the first polymerresin may be a thermally weldable polymer material, e.g. a castpolypropylene resin. The blocking metal may be, for example, aluminum.The second polymer resin may be a resin exhibiting excellent weatherresistance, such as a nylon resin, a polyethylene terephthalate resin,or a polyethylene naphthalate resin. However, the material is notlimited to the above examples.

In addition, the size of the battery case is greatly increased and thethickness of the battery case is greatly decreased according to a trendfor large capacity. Specifically, the base material, to which thepresent invention is applied, may have a thickness of 0.3 mm to 6 mm.

In a concrete example, the receiving part may have a side wallconfigured to have a stair-like structure including two or more stepsand the steps may have heights gradually decreased in a depth directionof the receiving part. In this structure, it is possible to minimize thechange in thickness of the receiving part due to elongation of the sheettype base material during formation of the receiving part since theheights of the steps are gradually decreased in the depth direction ofthe receiving part.

Specifically, in a case in which the stair-like structure includes nsteps, an n-th step may be located at the lowermost end of thestair-like structure in the depth direction of the receiving part, an(n−1)-th step may be located at the top of the n-th step, and the n-thstep may have a smaller height than the (n−1)-th step.

For example, in a case in which the stair-like structure includes threesteps, a first step may be located at the lowermost end of thestair-like structure in the depth direction of the receiving part, asecond step may be located at the top of the first step, and the secondstep may have a smaller height than the first step. In addition, a thirdstep may be located at the top of the second step and the third step mayhave a smaller height than the second step. Consequently, the heights ofthe first step, the second step, and the third step may be graduallydecreased.

In a concrete example, the height of the n-th step may be equivalent to50 to 90% of that of the (n−1)-th step. That is, the height of thesecond step may be equivalent to 50 to 90% of that of the first step andthe height of the third step may be equivalent to 50 to 90% of that ofthe second step.

In the present invention, therefore, the “heights of the respectivesteps are different from each other” may mean that an elongation ratioof the sheet type base material, from which the receiving part isformed, is changed during formation of the respective steps.

As a result, the thickness of the side wall of the receiving part at then-th step may be equivalent to 90 to 99% of that of the side wall of thereceiving part at the (n−1)-th step. That is, the thickness of the sidewall of the receiving part at the second step may be equivalent to 90 to99% of that of the side wall of the receiving part at the first step andthe thickness of the side wall of the receiving part at the third stepmay be equivalent to 90 to 99% of that of the side wall of the receivingpart at the second step. Consequently, the thickness of the side wall ofthe receiving part is relatively uniform although the receiving part isdeeply formed including a plurality of steps, thereby securing overalldurability of the battery case.

In accordance with another aspect of the present invention, there isprovided a method of manufacturing a battery cell having an electrodeassembly mounted in the battery case with the above-stated construction.

The battery cell manufacturing method includes (a) placing a sheet typebase material on a die having a groove, (b) pressing the sheet type basematerial into the groove of the die using a punch, an outside of whichis configured to have an asymmetric structure, such that wrinkles andchlorosis do not occur at corners of a receiving part formed from thesheet type base material, (c) mounting an electrode assembly in thereceiving part, and (d) placing a cover on the receiving part to sealthe receiving part, wherein the groove of the die is formed in a shapecorresponding to that of an outside of the punch such that the sheettype base material coincides with the shape of the outside of the punchwhen the sheet type base material contacts the punch and the groove ofthe die.

The punch may be formed in various three-dimensional shapes. In aconcrete example, a stair-like structure may be formed at the bottom ofthe punch.

In this case, the stair-like structure may be formed at the middle, oneside, or one corner of the bottom of the punch. Alternatively, otherstructures may be employed. For example, the stair-like structure may beformed at the bottom of the punch such that the stair-like structureslightly deviates from the middle of the bottom of the punch.

The battery case may be pressed by the punch having the stair-likestructure such that the receiving part of the battery case has astair-like structure corresponding to the punch.

According to circumstances, the battery cell manufacturing method mayfurther include forming a vacuum in a space defined between the die andthe sheet type base material between step (b) and step (c) such that thesheet type base material comes into tight contact with the groove of thedie.

To this end, an opening may be formed at one side of the groove of thedie to remove air from the space defined between the die and the sheettype base material. In this structure, the sheet type base material ispressed by the punch at step (b) and then a vacuum is formed in thespace defined between the die and the sheet type base material. As aresult, the sheet type base material is pulled to the groove of the die.Consequently, the sheet type base material may more accurately coincidewith the shape of the groove of the die. In this method, the punch andthe die apply force to the sheet type base material. Consequently, thereceiving part is formed so as to more accurately coincide with theshape of the punch and the die. In addition, force is more uniformlydistributed to the sheet type base material during pressing. As aresult, it is possible to manufacture the receiving part and the batterycase without wrinkles and chlorosis.

A vacuum may be applied to any pressing processes using other punches.In particular, the vacuum may be applied to all processes or only oneprocess using a specific punch.

In another concrete example, the die may be provided with a depressedpart configured to have a stair-like structure comprising an upper step,a middle step, and a lower step and the punch may include a first punchcorresponding to a shape of the upper step of the die, a second punchcorresponding to a shape of the middle step of the die, and a thirdpunch corresponding to a shape of the lower step of the die.

Specifically, the second punch may be formed in a shape corresponding tothe shapes of the upper step and the middle step of the die and thethird punch may be formed in a shape corresponding to the shapes of theupper step, the middle step, and the lower step of the die.

The battery case having the stair-like structure may be manufactured byplacing the sheet type base material on the die, (i) pressing the sheettype base material using the first punch to transfer the shape of theupper step of the die to the sheet type base material, (ii) pressing thesheet type base material using the second punch to transfer the shapesof the upper step and the middle step of the die to the sheet type basematerial, and (iii) pressing the sheet type base material using thethird punch to transfer the shapes of the upper step, the middle step,and the lower step of the die to the sheet type base material.

The battery case forming method as described above has an effect in thatwhen the battery case is formed to have a stair-like structure havingtwo or more steps, it is possible to maximally restrain concentration ofstress at corners of the respective steps. That is, when the side wallis formed at the receiving part to manufacture the battery case havingthe stair-like structure, a portion of the side wall is formed and thenanother portion of the side wall is formed. Consequently, it is possibleto minimize stress applied to the sheet type base material when thesheet type base material is elongated. In addition, the corners formingthe stair-like structure of the punch may be rounded to further improvesuch an effect, thereby further restraining concentration of stress.

In addition, in the same manner as in the previous example, the methodmay further include forming a vacuum in a space defined between the dieand the sheet type base material such that the sheet type base materialcomes into tight contact with the groove of the die after step (iii) isperformed.

In a further concrete example, the punch may include two or more puncheshaving different widths and heights, the die may be provided at aninside thereof with a stair-like structure including steps formed inshapes corresponding to the respective punches, and the receiving partmay have a stair-like structure formed by the punch and the die.

The stair-like structure of the receiving part may be formed by pressingperformed using one of the punches having the largest width and bypressing performed using the punches having the next largest widths. Thepressed depth of the sheet type base material may be decreased as thesheet type base material is pressed using the punches in reverse orderof width.

Specifically, in a case in which the number of the punches is n, thepressed depth of the sheet type base material formed by the n-th punchmay be equivalent to 60 to 90% of that of the sheet type base materialformed by the (n−1) th punch.

In this manufacturing method, it is possible to minimize the change inthickness of the receiving part due to elongation of the sheet type basematerial during formation of the receiving part since the heights of thesteps are decreased in the depth direction of the receiving part. As aresult, the thickness of the side wall of the receiving part isrelatively uniform, thereby securing overall durability of the batterycase.

In accordance with a further aspect of the present invention, there isprovided an apparatus for manufacturing the battery case with theabove-stated construction.

The battery case manufacturing apparatus includes a first die includinga punching die having a punch to press a battery case sheet mounted at abottom thereof and a stripper to fix the battery case sheet between thestripper and a stationary die during a drawing process and a second dieincluding a block die having a block corresponding to the punch mountedat a top thereof, the stationary die to fix the battery case sheetbetween the stripper and the stationary die, and a mounting die having adepressed part, in which the block die is variably mounted.

In the battery case manufacturing apparatus with the above-statedconstruction, a specific combination of various dies is operated to drawa portion of the battery case sheet at which an electrode assemblyreceiving part will be formed in a state in which the dies are in tightcontact with the battery case sheet above and below the battery casesheet during a series of processes. Consequently, it is possible tofundamentally prevent the occurrence of wrinkles at the outer surface ofthe battery case, which may occur as the sheet outside the receivingpart of the battery case is pushed into the inside of the receiving partduring manufacture of the battery case, thereby preventing productdefects.

Effects of the Invention

As is apparent from the above description, in the battery case accordingto the present invention and the manufacturing method of the same, atleast one corner and/or surface forming the shape of the receiving partis deformed to configure the stair-like structure. Consequently, it ispossible to provide a battery case including a receiving partcorresponding to an electrode assembly having various shapes, therebymaximizing the capacity of a device per unit volume.

In addition, the heights of the steps are gradually decreased in thedepth direction of the receiving part, and therefore, it is possible tominimize the change in thickness of the receiving part due to elongationof the sheet type base material during formation of the receiving part,thereby securing overall durability of the battery case.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is an exploded view showing a conventional lithium secondarybattery;

FIGS. 2 and 3 are partially enlarged views showing a receiving part ofFIG. 1;

FIG. 4 is a typical view showing a punch, a base material, and a die tomanufacture a battery case according to an embodiment of the presentinvention;

FIG. 5 is a vertical sectional view showing a battery case according toanother embodiment of the present invention;

FIG. 6 is a typical view showing a battery case manufacturing processaccording to another embodiment of the present invention;

FIGS. 7 and 8 are partially enlarged views of FIG. 6;

FIG. 9 is a typical view showing a process of manufacturing the batterycase of FIG. 5;

FIG. 10 is a vertical sectional view showing a battery casemanufacturing apparatus with a punch according to an embodiment of thepresent invention;

FIG. 11 is a view showing the structure of a first electrode groupaccording to an embodiment of the present invention;

FIG. 12 is a view showing the structure of a second electrode groupaccording to an embodiment of the present invention;

FIG. 13 is a typical view showing a stacked type electrode assemblyaccording to an embodiment of the present invention;

FIG. 14 is a typical view showing a fixing structure of the firstelectrode group of FIG. 12; and

FIG. 15 is a view showing a process of manufacturing a first electrodegroup according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Now, exemplary embodiments of the present invention will be described indetail with reference to the accompanying drawings. It should be noted,however, that the scope of the present invention is not limited by theillustrated embodiments.

FIG. 4 is a typical view showing a punch, a base material, and a die tomanufacture a battery case according to an embodiment of the presentinvention.

Referring to FIG. 4, a sheet type base material 200 is formed of alaminate sheet including a resin layer and a metal layer. Specifically,the base material includes an upper layer of a first polymer resin, anintermediate layer of a blocking metal, and a lower layer of a secondpolymer resin. During manufacture of a battery, the upper layer of thefirst polymer resin is thermally welded to each other, thereby achievingsealing.

Specifically, a method of manufacturing a battery case from a sheet typebase material 200 using a punch formed in a shape corresponding to areceiving part (not shown), in which an electrode assembly is mounted,is carried out as follows. First, the sheet type base material 200 isloaded on a die 300. The die 300 is provided with a groove (not shown)having an inside shape corresponding to the shape of a punch 100. As thebase material 200 is pressed by the punch 100, therefore, a receivingpart (not shown) is formed.

A method of forming the receiving part is carried out using one punch.The method of forming the receiving part includes a process of pressingthe punch to a sheet type base material to form the receiving part.Since the punch has a novel structure, the receiving part may be formedwithout wrinkles and chlorosis.

A stair-like structure 110 is formed at one corner of the bottom of thepunch 100 in a pressing direction (in a direction indicated by anarrow). In another embodiment, the stair-like structure 110 may beformed at the middle, one side, or one corner of the punch 100.

In addition, the method of manufacturing the battery case may furtherinclude a process of applying a vacuum to the die 300. Morespecifically, a vacuum may be formed in a space defined between thesheet type base material 200 and the die 300. In order to remove airfrom the space defined between the sheet type base material 200 and thedie 300, therefore, an opening (not shown) may be formed at one side ofthe groove of the die 300. As described above, the sheet type basematerial 200 is pressed by the punch 100 and a vacuum is formed in aspace defined between the sheet type base material 200 and the die 300.As a result, the sheet type base material 200 is pulled to the groove ofthe die 300. Consequently, the sheet type base material 200 may moreaccurately coincide with the shape of the groove of the die 300. In thismethod, the punch 100 and the die 300 apply force to the sheet type basematerial 200. Consequently, the receiving part is formed so as to moreaccurately coincide with the shape of the punch 100 and the die 300. Inaddition, more uniform force is distributed to the sheet type basematerial 200 during pressing. As a result, it is possible to manufacturethe receiving part and the battery case without wrinkles and chlorosis.

FIG. 5 is a vertical sectional view showing a battery case according toanother embodiment of the present invention.

Referring to FIG. 5, a battery case 40 includes a receiving part 410having a structure depressed in a direction indicated by an arrow. Thereceiving part 410 is configured to have a stair-like structureincluding a first step 411, a second step 412, and a third step 413. Thesteps 411, 412, and 413 have heights H1, H2, and H3, which are graduallydecreased in the direction indicated by the arrow. The height H2 of thesecond step 412 is equivalent to 50 to 90% of the height H1 of the firststep 411 and the height H3 of the third step 413 is equivalent to 50 to90% of the height H2 of the second step 412.

In addition, a thickness T2 of the second step 412 is equivalent to 90to 99% of a thickness T1 of the first step 411 and a thickness T3 of thethird step 413 is equivalent to 90 to 99% of the thickness T2 of thesecond step 412. As a result, the thickness of a side wall of thereceiving part 410 is relatively uniform, thereby securing overalldurability of the battery case 400.

FIG. 6 is a typical view showing a battery case manufacturing processaccording to another embodiment of the present invention. FIGS. 7 and 8are partially enlarged views of FIG. 6.

Referring to these drawings, three drawing processes 510, 520, and 530are carried out to manufacture a battery case 542 having three steps.Specifically, three punches 511, 521, and 531 corresponding to therespective steps are used with respect to a stationary die 501 in thethree drawing processes 510, 520, and 530. More specifically, thestationary die 510 is provided with a depressed part having a stair-likestructure including an upper step, a middle step, and a lower step. Oneof the three punches 511, 521, and 531, e.g. the punch 511 having thelargest width and the smallest height, first performs the drawingprocess 510. The outside of the first punch 511 is formed in a shapecorresponding to the upper step of the stationary die 501. Subsequently,the punch 521 having the second largest width and the second smallestheight performs the drawing process 520 and then the punch 531 havingthe smallest width and the largest height performs the drawing process530. The punches 521 and 531 used to perform the drawing processesfollowing the first drawing process 510 may be formed in shapescorresponding to the previously formed steps in addition to steps to beformed. That is, the outside of the next punch used after one step isformed corresponds to the previously formed step in addition to a stepto be formed. In this method, the shape of a base material that hasalready been elongated or deformed to form the step may be re-stampedduring the following processes. The outside of the second punch 521corresponds to the shape of the middle step of the stationary die 501 aswell as the shape of the upper step of the stationary die 501. Inaddition, the outside of the third punch 531 corresponds to the shapesof the upper step, the middle step, and the lower step of the stationarydie 501.

In this way, the drawing processes 510, 520, and 530 are performed forthe respective steps, thereby maximally restraining concentration ofstress at corners of the respective steps.

The apparatus shown in FIG. 6 is used as follows.

First, a sheet type base material 512 is placed on the stationary die501. The sheet type base material 512 is pressed between the stationarydie 501 and the first punch 511 such that the sheet type base material512 corresponds to the shape of the upper step of the stair-likestructure. As a result, the sheet type base material 512 is deformedinto a sheet type base material 522. The sheet type base material 522 ispressed between the stationary die 501 and the second punch 521 suchthat the sheet type base material 522 corresponds to the shapes of theupper step and the middle step of the stair-like structure. As a result,the sheet type base material 522 is deformed into a sheet type basematerial 532. The sheet type base material 532 is pressed between thestationary die 501 and the third punch 531 such that the sheet type basematerial 532 corresponds to the shapes of the upper step, the middlestep, and the lower step of the stair-like structure. As a result, thesheet type base material 532 is deformed into a sheet type base material542. Consequently, a receiving part having the stair-like structure isformed at the sheet type base material 542.

In addition, as shown in FIGS. 7 and 8, some of the corners forming theouter shapes of the punches 511, 521, and 531 and a stationary die 501,e.g. corners 502, 503, 504, and 505 contacting a battery case sheet (notshown), are rounded as indicated by reference symbol R.

Meanwhile, the method using the apparatus shown in FIG. 6 may include aprocess of applying a vacuum to the stationary die 501 as previouslydescribed in connection with the embodiment shown in FIG. 4. A vacuummay be applied to any pressing processes using other punches. Inparticular, the vacuum may be applied to all processes or only oneprocess using a specific punch.

FIG. 9 is a typical view showing a process of manufacturing the batterycase of FIG. 5.

Referring to FIG. 9, three drawing processes 610, 620, and 630 arecarried out to manufacture a battery case 642 having three steps 710,720, and 730. Three punches 611, 621, and 631 corresponding to therespective steps 710, 720, and 730 are used in the three drawingprocesses 610, 620, and 630. Specifically, in the first drawing process610, a sheet type base material 612 is placed and fixed on thestationary die 601 and the sheet type base material 612 is pressed usingthe first punch 611 to form a battery case 622 having the first step710. In the second drawing process 620, the battery case 622 is pressedusing the second punch 621, which has a smaller width and a largerheight than the first punch 611, to form a battery case 632 furtherhaving the second step 720. At this time, a depth D2 of the battery case632 formed by the second punch 621 is equivalent to 60 to 90% of a depthD1 of the battery case 622 formed by the first punch 611. In the thirddrawing process 630, the battery case 632 is pressed using the thirdpunch 631, which has a smaller width and a larger height than the secondpunch 621, to form a battery case 642 further having the third step 730.In the same manner as in the second drawing process 620, a depth D3 ofthe battery case 642 formed by the third punch 631 is equivalent to 60to 90% of the depth D2 of the battery case 632 formed by the secondpunch 621.

In this way, the drawing processes 610, 620, and 630 are performed forthe respective steps, thereby maximally restraining concentration ofstress at corners of the respective steps 710, 720, and 730.

In addition, as shown in FIGS. 7 and 8, some of the corners forming theouter shapes of the punches and the stationary die, e.g. cornerscontacting the battery case sheet, may be rounded.

FIG. 10 is a vertical sectional view showing a battery casemanufacturing apparatus with a punch according to an embodiment of thepresent invention.

Referring to FIG. 10, a battery case manufacturing apparatus 800includes a second die 820, to which a variable die 830 including a block821 is mounted, and a first die 810 to press a battery case sheet (notshown).

The first die 810 includes a punching die 813. To the lower side of thepunching die 813 of the first die 810 are mounted a punch 811 to form areceiving part of an electrode assembly (not shown) and a stripper 814having a first through opening 812, through which the punch 811 isinserted. The stripper 814 directly presses the battery case sheet (notshown).

The second die 820 includes a mounting die 824, to which the variabledie 830 is mounted and which has a depressed part 825, and a stationarydie 823 having a second through opening 822, through which the block 821of the variable die 830 is inserted. The block 821 corresponds to theshape of the punch 811.

Specifically, the depressed part 825, which is approximately configuredin a quadrangular shape, is formed at the mounting die 824 of the seconddie 820. At the depressed part 825 are formed two through holes 826,through which mounting shafts 832 of the variable die 830 are inserted,such that variable movement of the variable die 830 with respect to themounting die 824 is induced. Consequently, the variable die 830 ismounted in the depressed part 825 and the through holes 826 such thatthe variable die 830 can be variably reciprocated upward and downward.The battery case sheet (not shown) is supplied from the top of thesecond die 820 in one direction.

Meanwhile, four compression springs 833 are disposed between the blockdie 831 and the mounting die 824 such that the variable die 830 can bevariably reciprocated upward and downward in the second die 820 withease.

Although corners of the punch and dies are shown as being formed in aquadrangular shape, the punch and dies shown in FIG. 10 may be roundedin the same manner as shown in FIGS. 7 and 8.

Hereinafter, the operation of the battery case manufacturing apparatuswill be described in detail with reference to the above drawings.

First, a battery case sheet (not shown) is supplied to the top of thesecond die 820 of the battery case manufacturing apparatus 800 accordingto the present invention from the side of the battery case manufacturingapparatus. In addition, the first die 810 is moved downward to thesecond die 820 such that the stripper 814 of the first die 810 fixes thebattery case sheet in a tight contact state. Before punching or formingthe battery case sheet, the stripper 814 may independently move from thefirst die 810. When the first die 810 and the second die 820 move towardeach other, the stripper 814 may press the battery case sheet betweenthe stripper 814 and the stationary die 823 to fix the battery casesheet. The downward movement of the first die 810 is continued so thatthe punch 811 of the punching die 813 is inserted into the secondthrough opening 822 of the stationary die 824 while the punch 811 of thepunching die 813 presses the battery case sheet. Specifically, the punch811 of the punching die 813 is inserted into an opening of the block821. At this time, the block die 831 is elastically moved downward fromthe second through opening 822 and the depressed part 825 to themounting die 824 by the physical downward insertion of the punch 811such that a receiving part is formed at the battery case sheet bydrawing. Subsequently, the first die 810 is moved upward such that theblock die 831 returns to the original position thereof. As a result, thebattery case sheet having the receiving part formed thereat is separatedfrom the second die 820.

In addition, the method using the apparatus shown in FIG. 10 may includea process of applying a vacuum to the block 821 as previously describedin connection with the embodiment shown in FIG. 4.

Meanwhile, the electrode assembly may include cathodes, anodes, andseparators disposed respectively between the cathodes and the anodes. Inaddition, the electrode assembly may be configured to have a structurein which the cathodes and the anodes are respectively welded to twoelectrode terminals in a protruding state. The electrodes may be formedin a plate shape. The plate-shaped electrodes may be stacked along acentral axis of the electrode assembly. An asymmetric structure withrespect to the central axis of the electrode assembly may be formed atat least one side of the electrode assembly constituting the outercircumference of the electrode assembly. The surface area of eachplate-shaped electrode of the electrode assembly may be defined assurface area of a plane of each plate-shaped electrode perpendicular tothe central axis of the electrode assembly. The surface area of one ofthe plate-shaped electrodes may be smaller than that of anotherplate-shaped electrode. The electrode assembly may be configured to havea jelly roll type structure or a stacked type structure. However, thestructure of the electrode assembly is not particularly restricted.

The stacked type electrode assembly may include a first electrode groupconfigured to have a structure in which a cathode plate, an anode plate,and separator plates are laminated while being stacked such that thecathode plate or the anode plate and one of the separator plates arelocated at the outermost sides of the stacked type electrode assembly.

In addition, the stacked type electrode assembly may include a secondelectrode group configured to have a structure in which a cathode plate,an anode plate, and separator plates are laminated while being stackedsuch that the separator plates are located at the outermost sides of thestacked type electrode assembly.

For example, the first electrode group may be configured to have astructure in which a cathode plate, a separator plate, an anode plate,and a separator plate are laminated while being sequentially stacked ora structure in which an anode plate, a separator plate, a cathode plate,and a separator plate are laminated while being sequentially stacked.

The stacked type electrode assembly may be configured to have astructure in which only the first electrode groups are stacked.

The stacked type electrode assembly may include a third electrode groupconfigured to have a structure in which a cathode plate, an anode plate,and a separator plate are laminated while being stacked in a state inwhich the separator plate is disposed between the cathode plate and theanode plate such that the cathode plate and the anode plate are locatedat the outermost sides of the stacked type electrode assembly.

The stacked type electrode assembly may include a fourth electrode groupconfigured to have a structure in which a cathode plate or an anodeplate and a separator plate are laminated while being stacked.

The stacked type electrode assembly may be configured to have astructure in which only first electrode groups are stacked, a structurein which only second electrode groups are stacked, a structure in whichonly third electrode groups are stacked, a structure in which onlyfourth electrode groups are stacked, or a structure in which the first,second, third, and fourth electrode groups are combined.

The second electrode group may be stacked at the uppermost end or thelowermost end of the first electrode group.

In the structure in which only the second electrode groups are stacked,a cathode plate or an anode plate may be disposed between the secondelectrode groups.

A fixing member to more securely maintain the stack structure of thecathode plate, the separator plate, and the anode plate may be added tothe first electrode group to the fourth electrode group.

The fixing member may be an additional external member different fromthe first electrode group to the fourth electrode group. The fixingmember may be an adhesive tape or a bonding tape to cover a portion orthe entirety of the outside of each of the electrode groups.

The outside of each of the electrode groups may include sides, a top, afront, and a rear of each of the electrode groups.

The fixing member may be a portion of the separator plate constitutingthe first electrode group to the fourth electrode group. In this case,the ends of the separator plate may be thermally welded to fix the firstelectrode group to the fourth electrode group. However, the presentinvention is not limited thereto.

Ends of the separator plate may extend such that the separator plate hasa length larger than the size of the cathode plate and the anode plate,i.e. the horizontal length or the vertical length. The extending ends ofthe separator may be connected to each other by thermal welding.

The fixing member may include all members that are capable of fixing thefirst electrode group to the fourth electrode group.

In a case in which the stacked type electrode assembly is configured toinclude the first electrode group and the second electrode group, itpossible to improve productivity and yield as compared with the stackedtype electrode assembly configured to have a structure in which thecathode plate, the anode plate, and the separator plate are simplystacked.

In addition, the cathode plate, the separator plate, and the anode plateare laminated in unit of the first electrode group, and therefore, it ispossible to minimize expansion in volume of the stacked type electrodeassembly due to swelling.

In a case in which the stacked type electrode assembly is configured toinclude the first electrode group and the second electrode group,misalignment of the electrode assembly caused during a folding processis prevented and omission of processing equipment is possible. Inaddition, it is possible to form the first electrode group or the secondelectrode group using only one laminator. In addition, it is possible tomanufacture the stacked type electrode assembly by simple stacking.Consequently, damage to electrodes caused during the folding process maybe reduced and electrolyte wettability may be improved. Furthermore, asingle-sided organic and inorganic composite separator, e.g. a safetyreinforced separator (SRS), may be used as the separator plate exposedoutside. Consequently, cell thickness may be decreased and, at the sametime, processing cost may be reduced.

As shown in FIG. 11, a first electrode group is configured to have astructure in which a separator plate 310, a cathode plate 320, aseparator plate 330, and an anode plate 340 are laminated while beingsequentially stacked.

As shown in FIG. 12, a second electrode group is configured to have astructure in which a separator plate 410, an anode plate 420, and aseparator plate 430 are laminated while being sequentially stacked.

FIG. 13 shows a stacked type electrode assembly configured to have astructure in which the second electrode group of FIG. 12 is stacked onthe uppermost end of a first electrode group stack constituted by firstelectrode groups, one of which is shown in FIG. 11.

FIG. 14 shows an embodiment in which a fixing member T₁ is added to thefirst electrode group of FIG. 11. Specifically, the fixing member T₁ isadded to the side or the front of the first electrode group 300.

In order to secure stack stability of a simple stack structure, anadditional fixing member may be added to the side of the stack structureto fix the stack structure. The fixing member may be realized as a tapeT₁ surrounding the entire surface of the first electrode group 300 asshown in FIG. 14( a). Alternatively, the fixing member may be realizedas a fixing member T₂ to fix only each side of the electrode group 300as shown in FIG. 14( b).

FIG. 15 is a view typically showing a process of manufacturing the firstelectrode group according to the present invention.

As shown in FIG. 15, materials for a separator plate 310, a cathodeplate 320, a separator plate 330, and an anode plate 340 aresimultaneously loaded (using sheet type loading units). The material forthe cathode plate 320, which is used as a middle layer, is cut into adesigned size and is then loaded into laminators L₁ and L₂.Subsequently, the materials for the separator plates 310 and 330, whichare disposed under and above the material for the cathode plate 320, aresimultaneously loaded into the laminators L₁ and L₂. At the same time,the material for the anode plate 340 is loaded into the laminators L₁and L₂.

Subsequently, the laminators L₁ and L₂ form a structural body in whichthe two electrode plates and the two separator plates are laminated toeach other using heat and pressure, i.e. a first electrode group.Subsequently, a cutter C₃ cuts the structural body into a plurality offirst electrode groups. Afterwards, various inspection processes, suchas a thickness inspection (a), a vision inspection (b), and a shortcircuit inspection (c), may be performed with respect to each firstelectrode group.

Subsequently, each first electrode group manufactured as described aboveis fixed using a fixing member, and the first electrode groups arestacked to constitute a structural body in which the first electrodegroups are stacked. Subsequently, the second electrode group shown inFIG. 12 is stacked on the structural body and then the second electrodegroup and the structural body are fixed using a fixing member, therebycompleting a stacked type electrode assembly.

The number of electrode groups having different plane sizes constitutingthe electrode assembly may be flexibly adjusted by those skilled in theart based on the shape or required capacity of a device in which theelectrode groups are mounted. For example, the electrode assembly mayinclude two or three electrode groups. Alternatively, the electrodeassembly may include four or more electrode groups.

Although the exemplary embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A battery case comprising a receiving part having an electrodeassembly mounted therein, wherein the receiving part, which is formed bydeforming a sheet type base material, is configured to have a stair-likestructure in which at least one corner and/or surface forming a shape ofthe receiving part is deformed.
 2. The battery case according to claim1, wherein the base material is formed of a laminate sheet comprising aresin layer and a metal layer.
 3. The battery case according to claim 2,wherein the base material comprises an upper layer of a first polymerresin, an intermediate layer of a blocking metal, and a lower layer of asecond polymer resin.
 4. The battery case according to claim 1, whereinthe base material has a thickness of 0.3 mm to 6 mm.
 5. The battery caseaccording to claim 1, wherein the receiving part has a side wallconfigured to have a stair-like structure comprising two or more steps,and the steps have heights gradually decreased in a depth direction ofthe receiving part.
 6. The battery case according to claim 5, wherein,in a case in which the stair-like structure comprises n steps, an n-thstep is located at a lowermost end of the stair-like structure in thedepth direction of the receiving part, an (n−1)-th step is located at atop of the n-th step, and the n-th step has a smaller height than the(n−1)-th step.
 7. The battery case according to claim 6, wherein theheight of the n-th step is equivalent to 50 to 90% of that of the(n−1)-th step.
 8. The battery case according to claim 6, wherein athickness of the side wall of the receiving part at the n-th step isequivalent to 90 to 99% of that of the side wall of the receiving partat the (n−1)-th step.
 9. A method of manufacturing a battery cell havingan electrode assembly mounted in a battery case according to claim 1,the method comprising: (a) placing a sheet type base material on a diehaving a groove; (b) pressing the sheet type base material into thegroove of the die using a punch, an outside of which is configured tohave an asymmetric structure, such that wrinkles and chlorosis do notoccur at corners of a receiving part formed from the sheet type basematerial (c) mounting an electrode assembly in the receiving part; and(d) placing a cover on the receiving part to seal the receiving part,wherein the groove of the die is formed in a shape corresponding to thatof an outside of the punch such that the sheet type base materialcoincides with the shape of the outside of the punch when the sheet typebase material contacts the punch and the groove of the die.
 10. Themethod according to claim 9, wherein a stair-like structure is formed ata bottom of the punch.
 11. The method according to claim 10, wherein thestair-like structure is formed at a middle, one side, or one corner ofthe bottom of the punch.
 12. The method according to claim 9, furthercomprising forming a vacuum in a space defined between the die and thesheet type base material such that the sheet type base material comesinto tight contact with the groove of the die.
 13. The method accordingto claim 9, wherein the die is provided with a depressed part configuredto have a stair-like structure comprising an upper step, a middle step,and a lower step, and the punch comprises a first punch corresponding toa shape of the upper step of the die, a second punch corresponding to ashape of the middle step of the die, and a third punch corresponding toa shape of the lower step of the die.
 14. The method according to claim13, wherein the second punch is formed in a shape corresponding to theshapes of the upper step and the middle step of the die, and the thirdpunch is formed in a shape corresponding to the shapes of the upperstep, the middle step, and the lower step of the die.
 15. The methodaccording to claim 14, further comprising: (i) pressing the sheet typebase material using the first punch to transfer the shape of the upperstep of the die to the sheet type base material; (ii) pressing the sheettype base material using the second punch to transfer the shapes of theupper step and the middle step of the die to the sheet type basematerial; and (iii) pressing the sheet type base material using thethird punch to transfer the shapes of the upper step, the middle step,and the lower step of the die to the sheet type base material.
 16. Themethod according to claim 15, further comprising forming a vacuum in aspace defined between the die and the sheet type base material such thatthe sheet type base material comes into tight contact with the groove ofthe die.
 17. The method according to claim 9, wherein corners of anoutside of the punch and corners of an inside of the die are rounded.18. The method according to claim 9, wherein the punch comprises two ormore punches having different widths and heights, the die is provided atan inside thereof with a stair-like structure comprising steps formed inshapes corresponding to the respective punches, and the receiving parthas a stair-like structure formed by the punch and the die.
 19. Themethod according to claim 18, wherein the stair-like structure of thereceiving part is formed by pressing performed using one of the puncheshaving largest width and then by pressing performed using the puncheshaving next largest widths.
 20. The method according to claim 19,wherein the pressed depth of the sheet type base material is decreasedas the sheet type base material is pressed using the punches in reverseorder of width.
 21. The method according to claim 20, wherein, in a casein which the number of the punches is n, the pressed depth of the sheettype base material formed by the n-th punch is equivalent to 60 to 90%of that of the sheet type base material formed by the (n−1) th punch.22. The method according to claim 21, wherein corners of outsides of thepunches and corners of an inside of the die are rounded.
 23. Anapparatus for manufacturing a battery case according to claim 1, theapparatus comprising: a first die comprising a punching die having apunch to press a battery case sheet mounted at a bottom thereof and astripper to fix the battery case sheet between the stripper and astationary die during a drawing process; and a second die comprising ablock die having a block corresponding to the punch mounted at a topthereof, the stationary die to fix the battery case sheet between thestripper and the stationary die, and a mounting die having a depressedpart, in which the block die is variably mounted.